@Gertjan Hello again, im back after 15 days because I needed to recompile everything with the latest FreeBSD kernel. So everything is now compatible for FreeBSD 15.0 (which is the kernel of pfSense).
The new file reports as :
/usr/local/sbin/dhcp6c: ELF 64-bit LSB executable, ARM aarch64, version 1 (FreeBSD), dynamically linked, interpreter /libexec/ld-elf.so.1, for FreeBSD 15.0 (1500012), FreeBSD-style, stripped
You can see how I have done the steps to compile it here : https://github.com/Superpaul209/dhcp6c-armv7
Everything is up to date and you can find the binaries on this GitHub for arm64 and armv7 (for those who would like them if they are living in France).
The installation was successful on each pfSense, after a reboot Im now having an IPv6 ! The problem was therefore one of compatibility with the kernel version which was too old.
Thanks for your ideas and your help, it has solved my issue 😊